Inter-cervical facet implant and method

ABSTRACT

Systems and method in accordance with the embodiments of the present invention can include an implant for positioning within a cervical facet joint for distracting the cervical spine, thereby increasing the area of the canals and openings through which the spinal cord and nerves must pass, and decreasing pressure on the spinal cord and/or nerve roots. The implant can be inserted laterally or posteriorly.

CLAIM OF PRIORITY

This application claims priority to United States ProvisionalApplication, entitled, INTER-CERVICAL FACET IMPLANT AND METHOD filedDec. 13, 2004, Ser. No. 60/635,453, which is incorporated herein byreference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.11/053,399, entitled INTER-CERVICAL FACET IMPLANT AND METHOD, filed Feb.8, 2005; U.S. patent application Ser. No. 11/053,735, entitledINTER-CERVICAL FACET IMPLANT AND METHOD, filed Feb. 8, 2005; and U.S.patent application Ser. No. 11/053,346, entitled INTER-CERVICAL FACETIMPLANT AND METHOD, filed Feb. 8, 2005 which are each incorporatedherein in full, by reference.

TECHNICAL FIELD

This invention relates to interspinous process implants.

BACKGROUND OF THE INVENTION

The spinal column is a bio-mechanical structure composed primarily ofligaments, muscles, vertebrae and intervertebral disks. Thebio-mechanical functions of the spine include: (1) support of the body,which involves the transfer of the weight and the bending movements ofthe head, trunk and arms to the pelvis and legs, (2) complexphysiological motion between these parts, and (3) protection of thespinal cord and the nerve roots.

As the present society ages, it is anticipated that there will be anincrease in adverse spinal conditions which are characteristic of olderpeople. By way of example only, with aging comes an increase in spinalstenosis (including, but not limited to, central canal and lateralstenosis), and facet arthropathy. Spinal stenosis results in a reductionforaminal area (i.e., the available space for the passage of nerves andblood vessels) which compresses the cervical nerve roots and causesradicular pain. Humpreys, S. C. et al., Flexion and traction effect onC5-C6 foraminal space, Arch. Phys. Med. Rehabil., vol. 79 at 1105(September 1998). Another symptom of spinal stenosis is myelopathy,which results in neck pain and muscle weakness. Id. Extension andipsilateral rotation of the neck further reduces the foraminal area andcontributes to pain, nerve root compression, and neural injury. Id.;Yoo, J. U. et al., Effect of cervical spine motion on the neuroforaminaldimensions of human cervical spine, Spine, vol. 17 at 1131 (Nov. 10,1992). In contrast, neck flexion increases the foraminal area. Humpreys,S. C. et al., supra, at 1105.

In particular, cervical radiculopathy secondary to disc herniation andcervical spondylotic foraminal stenosis typically affects patients intheir fourth and fifth decade, and has an annual incidence rate of 83.2per 100,000 people (based on 1994 information). Cervical radiculopathyis typically treated surgically with either an anterior cervicaldiscectomy and fusion (“ACDF”) or posterior laminoforaminotomy (“PLD”),with or without facetectomy. ACDF is the most commonly performedsurgical procedure for cervical radiculopathy, as it has been shown toincrease significantly the foraminal dimensions when compared to a PLF.

It is desirable to eliminate the need for major surgery for allindividuals, and in particular, for the elderly. Accordingly, a needexists to develop spine implants that alleviate pain caused by spinalstenosis and other such conditions caused by damage to, or degenerationof, the cervical spine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a lateral view of two adjacent cervical vertebrae andspinous processes, highlighting the cervical facet joint.

FIG. 2 depicts a lateral view of the cervical spine with spinalstenosis.

FIG. 3A depicts correction of cervical stenosis or other ailment with awedge-shaped embodiment of the implant of the invention positioned inthe cervical facet joint.

FIG. 3B depicts correction of cervical kyphosis or loss of lordosis witha wedge-shaped embodiment of the invention with the wedge positioned inthe opposite direction as that depicted in FIG. 3A.

FIG. 4 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention including a screwfixation device for attaching to a single vertebra.

FIG. 5 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising screwfixation of two implants, one implant fixed to each of two adjacentvertebrae.

FIG. 6 shows cervical spine kyphosis, or loss of lordosis.

FIG. 7 shows correction of cervical kyphosis, or loss of lordosis, witha further embodiment of the implant of the invention comprising twofacet implants with screw fixation.

FIG. 8 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetimplant and a keel.

FIG. 9 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising facetimplant, a keel, and screw fixation.

FIG. 10 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetimplant with teeth.

FIG. 11 depicts correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetimplant with teeth and screw fixation.

FIG. 12 depicts correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants having bony ingrowth surfaces.

FIG. 13 depicts correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants having bony ingrowth surfaces and posterior alignment guide.

FIG. 14 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants with increased facet joint contact surfaces.

FIG. 15 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants having bony ingrowth surfaces and screw fixation.

FIG. 16 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetimplants with articular inner surfaces.

FIG. 17 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetjoint implant with a roller.

FIG. 18 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising a facetjoint implant with a plurality of rollers.

FIG. 19 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetjoint implants, screw fixation, and elastic restraint.

FIG. 20 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetjoint implants, screw fixation, and spring restraint.

FIG. 21 shows correction of cervical stenosis or other ailment with afurther embodiment of the implant of the invention, comprising two facetjoint implants, screw fixation, and magnetic restraint.

FIG. 22A shows a perspective view of a further embodiment of implant ofthe invention.

FIG. 22B shows a perspective exploded view of the embodiment of theinvention shown in FIG. 22A.

FIG. 23A depicts a posterior view of the embodiment of the implant ofthe invention shown in FIG. 22A.

FIG. 23B shows a posterior view of a locking plate of the embodiment ofthe implant of the invention shown in FIG. 22A.

FIG. 24A depicts a lateral side view of the embodiment of the implant ofthe invention shown in FIG. 22A.

FIG. 24B shows a lateral side view of the keel of the locking plate ofthe embodiment of the implant of the invention shown in FIG. 22A.

FIG. 25A shows a perspective view of a further embodiment of the implantof the invention.

FIG. 25B shows a side view of the embodiment of the implant of theinvention in FIG. 25A, having a curved, uniformly-thick artificial facetjoint spacer or inter-facet spacer including a tapered end.

FIG. 26A shows an anterior perspective view of a further embodiment ofthe implant of the invention.

FIG. 26B shows a posterior perspective view of the embodiment of theimplant of the invention depicted in FIG. 26A.

FIG. 27A depicts a side view of the embodiment of the implant of theinvention shown in FIGS. 26A and 26B, implanted in the cervical spine.

FIG. 27B shows a posterior view of the embodiment of the implant of theinvention shown in FIGS. 26A, 26B, and 27A, implanted in the cervicalspine.

FIG. 28A depicts a posterior perspective view of a further embodiment ofthe implant of the invention.

FIG. 28B depicts a side view of the embodiment of the implant of theinvention shown in FIG. 28A.

FIG. 29A depicts a side view of an embodiment of a sizing tool of theinvention.

FIG. 29B depicts a top view of an embodiment of the sizing tool of theinvention depicted in FIG. 29A.

FIG. 29C depicts a perspective view of an embodiment of the sizing toolof the invention depicted in FIGS. 29A-B.

FIG. 29D depicts a side view of the head of the sizing tool of theinvention depicted in FIG. 29A

FIG. 29E depicts a cross-sectional view of the head of the sizing toolof the invention depicted in FIGS. 29A-C.

FIG. 30 is a flow diagram of an embodiment of a method of the invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide for a minimally invasivesurgical implantation method and apparatus for cervical spine implantsthat preserves the physiology of the spine. In particular, embodimentsprovide for distracting the cervical spine to increase the foraminaldimension in extension and neutral positions. Such implants distract, orincrease the space between, the vertebrae to increase the foraminal areaor dimension, and reduce pressure on the nerves and blood vessels of thecervical spine. In a specific preferred embodiment, an implantedinterfacet spacer of 1.5 mm to 2.5 mm in width can result in interfacetdistraction that increases foraminal dimension in extension and neutral.Other interfacet spacer dimensions also are contemplated by theinvention described herein below. The present embodiments also preservemobility of the facet joints.

Further embodiments of the present invention accommodate the distinctanatomical structures of the spine, minimize further trauma to thespine, and obviate the need for invasive methods of surgicalimplantation. Embodiments of the present invention also address spinalconditions that are exacerbated by spinal extension.

FIG. 1 shows a simplified diagram of a portion of the cervical spine,focusing on a cervical facet joint 1 formed between two adjacentcervical vertebrae. The spinous processes 3 are located posteriorly andthe vertebral bodies 5 are located anteriorly, and a nerve root canal 7is visible.

FIG. 2 depicts cervical foraminal stenosis. From the drawing, the nerveroot canal 7 is narrowed relative to the nerve root canal 7 depicted inFIG. 1. The spinal canal and/or intervertebral foramina also can benarrowed by stenosis. The narrowing can cause compression of the spinalcord and nerve roots.

FIG. 3A shows a first embodiment 100 of the present invention, which ismeant to distract at least one facet joint, in order to increase thedimension of the neural foramen while retaining facet joint mobility.The wedge-shaped embodiment or inter-facet spacer 100 is a wedge-shapedimplant that can be positioned in the cervical facet joint 101 todistract the joint and reverse narrowing of the nerve root canal 107. Inthis embodiment or inter-facet spacer 100, the implant is positionedwith the narrow portion of the wedge facing anteriorly. However, it isalso within the scope of the present invention to position embodiment orinter-facet spacer 100 (FIG. 3B) with the wide portion of the wedgefacing anteriorly, to correct for cervical kyphosis or loss of cervicallordosis.

It is to be understood that implants in accordance with the presentinvention, and/or portions thereof can be fabricated from somewhatflexible and/or deflectable material. In these embodiments, the implantand/or portions thereof can be made out of a polymer, such as athermoplastic. For example, in one embodiment, the implant can be madefrom polyketone, known as polyetheretherketone (“PEEK”). Still morespecifically, the implant can be made from PEEK 450G, which is anunfilled PEEK approved for medical implantation available from Victrexof Lancashire, Great Britain. Other sources of this material includeGharda located in Panoli, India. PEEK has the following approximateproperties:

Property Value Density 1.3 g/cc Rockwell M  99 Rockwell R 126 TensileStrength  97 MPa Modulus of Elasticity 3.5 GPa Flexural Modulus 4.1 GPa

The material specified has appropriate physical and mechanicalproperties and is suitable for carrying and spreading a physical loadbetween the adjacent spinous processes. The implant and/or portionsthereof can be formed by extrusion, injection, compression moldingand/or machining techniques.

In some embodiments, the implant can comprise, at least in part,titanium or stainless steel, or other suitable implant material which isradiopaque, and at least in part a radiolucent material that does notshow up under x-ray or other type of imaging. The physician can have aless obstructed view of the spine under imaging, than with an implantcomprising radiopaque materials entirely. However, the implant need notcomprise any radiolucent materials.

It should be noted that the material selected also can be filled. Forexample, other grades of PEEK are also available and contemplated, suchas 30% glass-filled or 30% carbon-filled, provided such materials arecleared for use in implantable devices by the FDA, or other regulatorybody. Glass-filled PEEK reduces the expansion rate and increases theflexural modulus of PEEK relative to that unfilled PEEK. The resultingproduct is known to be ideal for improved strength, stiffness, orstability. Carbon-filled PEEK is known to enhance the compressivestrength and stiffness of PEEK and to decrease its expansion rate.Carbon-filled PEEK offers wear resistance and load-carrying capability.

In this embodiment or inter-facet spacer 100, the implant ismanufactured from PEEK, available from Victrex. As will be appreciated,other suitable similarly biocompatible thermoplastic or thermoplasticpolycondensate materials that resist fatigue, have good memory, areflexible, and/or deflectable, have very low moisture absorption, andgood wear and/or abrasion resistance, can be used without departing fromthe scope of the invention. The spacer also can be comprised ofpolyetherketoneketone (“PEKK”). Other material that can be used includepolyetherketone (“PEK”), polyetherketoneetherketoneketone (“PEKEKK”),and polyetheretherketoneketone (“PEEKK”), and generally apolyaryletheretherketone. Further, other polyketones can be used as wellas other thermoplastics. Reference to appropriate polymers that can beused in the implant can be made to the following documents, all of whichare incorporated herein by reference. These documents include: PCTPublication WO 02/02158 A1, dated Jan. 10, 2002, entitled“Bio-Compatible Polymeric Materials”; PCT Publication WO 02/00275 A1,dated Jan. 3, 2002, entitled “Bio-Compatible Polymeric Materials; and,PCT Publication WO 02/00270 A1, dated Jan. 3, 2002, entitled“Bio-Compatible Polymeric Materials.” Other materials such as Bionate®,polycarbonate urethane, available from the Polymer Technology Group,Berkeley, Calif., may also be appropriate because of the good oxidativestability, biocompatibility, mechanical strength and abrasionresistance. Other thermoplastic materials and other high molecularweight polymers can be used.

Turning now to FIG. 4, the embodiment 200 of the implant has a jointinsert or inter-facet spacer 210, also herein referred to as anartificial facet joint spacer or inter-facet spacer, that is positionedin the cervical facet joint 101. The joint insert or inter-facet spacer210 can be wedge-shaped with the narrow part of the wedge facinganteriorly. Alternatively, the joint insert or inter-facet spacer 210need not be wedge-shaped but can be of substantially uniform thickness,the thickness determined by an individual patient's need for distractionof the cervical facet joint 201. As with embodiment 100, one objectiveof this embodiment is facet joint distraction, and joint mobility afterimplantation. The joint insert or inter-facet spacer 210 is continuouswith a posterior sheath 220 bent at an angle from the joint insert orinter-facet spacer 210 to align substantially parallel with the bone.The posterior sheath can lie against the lamina, preferably against thelateral mass. The posterior sheath 220 can have a bore 230 which canaccept a bone screw 240. Alternatively, the bore 230 can accept anyother appropriate and/or equivalent fixation device capable of fixingthe embodiment 200 to the spine. The device is thereby affixed to thevertebra, preferably by fixing to the lateral mass.

FIG. 5 shows embodiment 300, which is the use of two embodiments 200,each fixed to one of two adjacent cervical vertebrae. As with embodiment200, the implanted facet joint is distracted and joint mobility isretained. A joint insert or inter-facet spacer 310 from each of the twoimplants is inserted and positioned in the cervical facet joint 301. Inthis embodiment, the joint inserts or inter-facet spacers 310 aresubstantially flat and parallel to each other and are not wedge-shaped.Alternatively, the joint inserts or inter-facet spacers 310 can togetherdefine a wedge-shaped insert that is appropriate for the patient. Thetwo joint inserts or inter-facet spacers 310 combined can have, by wayof example, the shape of the joint insert or inter-facet spacer 210 inFIG. 4. Embodiment 300 then can be fixed to the spine with a screw 340or any other appropriate fixation device, inserted through a bore 330 inthe posterior sheath 320. The posterior sheath 320 can be threaded toaccept a screw. The screw can be embedded in the lamina, preferably inthe lateral mass, where possible.

It is within the scope of the present invention to use and/or modify theimplants of the invention to correct cervical spine kyphosis, or loss oflordosis. FIG. 6 depicts a cervical spine lordosis. FIG. 7 demonstratesan embodiment 400 which contemplates positioning two implants to correctfor this spinal abnormality while retaining facet joint mobility. Thejoint insert or inter-facet spacer 410 of each implant is shaped so thatit is thicker at its anterior portion. Alternatively, the implants canbe shaped to be thicker at the posterior ends, for example as depictedin FIG. 3A. The posterior sheath 420 of each implant is bent at an anglefrom the joint insert or inter-facet spacer 410 to be positionedadjacent to the lateral mass and/or lamina, and has a bore 430 to accepta screw 440 or other appropriate and/or equivalent fixation means to fixthe embodiment 400 to the spine, preferably to the lateral mass. Theplacement of two joint inserts or inter-facet spacers 410 in thecervical facet joint 401 distracts the facet joint, which shifts andmaintains the vertebrae into a more anatomical position to preserve thephysiology of the spine.

FIG. 8 shows a further embodiment 500 of the implant of the invention,wherein the joint insert or inter-facet spacer 510 has a keel 550 on anunderside of the joint insert or inter-facet spacer 510. The keel 550can be made of the same material or materials set forth above. Thesurfaces of the keel 550 can be roughened in order to promote boneingrowth to stabilize and fix the implant 500. In other embodiments, thekeel 550 can be coated with materials that promote bone growth such as,for example, bone morphogenic protein (“BMP”), or structural materialssuch as hyaluronic acid “HA,” or other substances which promote growthof bone relative to and into the keel 550.

The keel 550 can be embedded in the facet bone, to facilitate implantretention. The keel 550 can be placed into a channel in the facet bone.The channel can be pre-cut. Teeth (not shown), preferably positionedposteriorly, also may be formed on the keel 550 for facilitatingretention of the implant 500 in the cervical facet joint 501. As notedabove, the joint insert or inter-facet spacer 510 can be substantiallyflat or wedge-shaped, depending upon the type of distraction needed,i.e., whether distraction is also necessary to correct abnormalcurvature or lack of curvature in the cervical spine. Because the jointis not fused, mobility is retained, as with the embodiments describedabove and herein below.

FIG. 9 illustrates that a further embodiment 600 of the implant of theinvention can have both screw fixation and a keel 650 for stability andretention of the implant 600. On embodiment 600, the joint insert orinter-facet spacer 610 is continuous with a posterior sheath 620 havinga bore hole 630 to accept a screw 640 which passes through the bore 630and into the bone of the vertebrae, preferably into the lateral mass, orthe lamina. The bore 630 can be threaded or not threaded where it is toaccept a threaded screw or equivalent device. Alternatively, the bore630 need not be threaded to accept a non-threaded equivalent device. Thekeel 650 is connected with the joint insert or inter-facet spacer 610and embeds in the bone of the cervical facet joint 601 to promoteimplant retention.

A further alternative embodiment 700 is illustrated in FIG. 10. In thisembodiment 700, the joint insert or inter-facet spacer 710 has on alower side at least one tooth 760. It should be clear to one of ordinaryskill in the art that a plurality of teeth 760 is preferable. The teeth760 are able to embed in the bone of the cervical facet joint 701 tofacilitate retention of the implant 700 in the joint 701. The teeth 760can face in a direction substantially opposite the direction ofinsertion, for retention of the implant 700. As above, the joint insertor inter-facet spacer 710 can be wedge-shaped or substantially even inthickness, depending upon the desired distraction. Because the implantdistracts and is retained without fusion, facet joint mobility isretained.

FIG. 11 depicts a further embodiment 800 of the implant of theinvention. In this embodiment 800, the joint insert or inter-facetspacer 810 is continuous with a posterior sheath 820 having a bore 830for accepting a fixation device 840, as described above. The fixationdevice 840 can be a screw which fits into a threaded bore 830;alternatively, the fixation device 830 can be any other compatible andappropriate device. This embodiment 800 further combines at least onetooth 860 on an underside of the joint insert or inter-facet spacer 810with the posterior sheath 820, bore 830 and fixation device 840 toaddress fixation of the implant 800 in a cervical facet joint 801. Itwill be recognized by one of ordinary skill in the art that the implant800 can have a plurality of teeth 860 on the underside of the jointinsert or inter-facet spacer 810.

FIG. 12 shows yet another embodiment 900 of an implant of the presentinvention. In this embodiment 900, the joint inserts or inter-facetspacers 910 of two implants 900 are positioned in a cervical facet joint901. As described above, the joint inserts or inter-facet spacers 910can be wedge-shaped as needed to restore anatomical curvature of thecervical spine and to distract, or the joint inserts or inter-facetspacers 910 can be of substantially uniform thickness. The implants 900each comprise a joint insert or inter-facet spacer 910 with an outersurface 970 that interacts with the bone of the cervical facet joint901. On the upper implant 900, the surface 970 that interacts with thebone is the upper surface 970 and on the lower implant 900, the surface970 that interacts with the bone is the lower surface 970. Each surface970 can comprise a bone ingrowth surface 980 to create a porous surfaceand thereby promote bone ingrowth and fixation. One such treatment canbe with plasma spray titanium, and another, with a coating of sinteredbeads. Alternatively, the implant 900 can have casted porous surfaces970, where the porous surface is integral to the implant 900. As afurther alternative, the surfaces 970 can be roughened in order topromote bone ingrowth into these defined surfaces of the implants 900.In other embodiments, the surfaces 970 can be coated with materials thatpromote bone growth such as for example bone morphogenic protein(“BMP”), or structural materials such as hyaluronic acid (“HA”), orother substances which promote growth of bone on other external surfaces970 of the implant 900. These measures facilitate fixation of theimplants 900 in the facet joint, but do not result in fusion of thejoint, thereby retaining facet joint mobility, while also accomplishingdistraction of the joint.

FIG. 13 depicts yet another embodiment 1000 of the implant of thepresent invention. In this embodiment 1000, the joint inserts orinter-facet spacers 1010 of two implants 1000 are positioned in acervical facet joint 1001. As described above, the joint inserts orinter-facet spacers 1010 can be wedge-shaped as needed to restoreanatomical curvature of the cervical spine and to distract, or the jointinserts or inter-facet spacers 1010 can be of substantially uniformthickness. The implants 1000 each comprise a joint insert or inter-facetspacer 1010 with an outer surface 1070 that interacts with the bone ofthe cervical facet joint 1001. On the upper implant 1000, the surface1070 that interacts with the bone is the upper surface and on the lowerimplant 1000, the surface 1070 that interacts with the bone is the lowersurface. As set forth above, each outer surface 1070 can comprise a boneingrowth surface 1080 to create a porous surface and thereby promotebone ingrowth and fixation, without facet joint fusion and loss ofmobility. In one preferred embodiment, the bone ingrowth surface 1080can be created with plasma spray titanium, and/or with a coating ofsintered beads. In an alternative preferred embodiment, the implant 1000can have casted porous surfaces 1070, where the porous surface isintegral to the implant 1000. In a further alternative preferredembodiment, the surfaces 1070 can be roughened in order to promote boneingrowth into these defined surfaces of the implants 1000. In otherpreferred embodiments, the surfaces 1070 can be coated with materialsthat promote bone growth such as for example BMP, or structuralmaterials such as HA, or other substances which promote growth of boneon other external surfaces 1070 of the implant 1000.

The implant 1000 can have a posterior alignment guide 1090. Theposterior alignment guides 1090 of each implant 1000 can be continuouswith the joint inserts or inter-facet spacers 1010. The posterioralignment guides substantially conform to the bone of the vertebrae whenthe joint inserts or inter-facet spacers 1010 are inserted into thecervical facet joint 1001. The posterior alignment guides 1090 are usedto align the implants 1000 so that the joint inserts or inter-facetspacers 1010 contact each other and not the bones of the cervical facetjoint 1001 when the joint inserts or inter-facet spacers 1010 arepositioned in the cervical facet joint 1001.

FIG. 14 depicts a further embodiment 1100 of the implant of the presentinvention. In this embodiment 1100, the joint inserts or inter-facetspacers 1110 of two implants 1100 are inserted into the cervical facetjoint 1101. Each of the joint inserts or inter-facet spacers 1110 iscontinuous with a cervical facet joint extender or facet-extendingsurface 1192. The bone contacting surfaces 1170 of the joint inserts orinter-facet spacers 1110 are continuous with, and at an angle to, thebone contacting surfaces 1193 of the cervical facet joint extenders1192, so that the cervical facet joint extenders 1192 conform to thebones of the vertebrae exterior to the cervical facet joint 1101. Theconformity of the cervical facet joint extenders 1192 is achieved forexample by forming the cervical facet joint extenders 1192 so that whenthe joint inserts or inter-facet spacers 1110 are positioned, thecervical facet joint extenders 1192 curve around the bone outsider thecervical facet joint 1101.

The cervical facet joint extenders have a second surface 1184 that iscontinuous with the joint articular surfaces 1182 of the joint insertsor inter-facet spacers 1110. The second surfaces 1184 extend the implant1100 posteriorly to expand the joint articular surfaces 1182 and therebyto increase contact and stability of the spine at least in the region ofthe implants 1100. It is to be understood that such facet jointextenders 1192 can be added to the other embodiments of the inventiondescribed and depicted herein.

The embodiment depicted in FIG. 15 shows two implants 1200 positioned ina cervical facet joint 1201, having bony ingrowth surfaces as onepreferred method of fixation, and using screws as another preferredmethod of fixation. In this embodiment, each of two implants 1200 has ajoint insert or inter-facet spacer 1210 positioned in a cervical facetjoint 1201. As described above, the joint inserts or inter-facet spacers1210 can be wedge-shaped as needed to restore anatomical curvature ofthe cervical spine and to distract, or the joint inserts or inter-facetspacers 1210 can be of substantially uniform thickness. The implants1200 each comprise a joint insert or inter-facet spacer 1210 with anouter surface 1270 that interacts with the bone of the cervical facetjoint 1001. On the upper implant 1200, the surface 1270 that interactswith the bone is the upper surface and on the lower implant 1200, thesurface 1270 that interacts with the bone is the lower surface. As setforth above, each outer surface 1270 can comprise a bone ingrowthsurface 1280 to create a porous surface and thereby promote boneingrowth and fixation. In one preferred embodiment, the bone ingrowthsurface 1280 can be created with plasma spray titanium, and/or with acoating of sintered beads. In an alternative preferred embodiment, theimplant 1200 can have casted porous surfaces 1270, where the poroussurface is integral to the implant 1200. In a further alternativeembodiment, the surfaces 1270 can be roughened in order to promote boneingrowth into these defined surfaces of the implants 1200. In otherpreferred embodiments, the surfaces 1270 can be coated with materialsthat promote bone growth such as for example BMP, or structuralmaterials such as HA, or other substances which promote growth of boneon other external surfaces 1270 of the implant 1200.

Screw fixation or other appropriate fixation also can be used withimplants 1200 for fixation in the cervical facet joint 1201. The jointinsert or inter-facet spacer 1210 is continuous with a posterior sheath1220 bent at an angle from the joint insert or inter-facet spacer 1210to align substantially parallel with the bone, preferably the lateralmass or lamina. The posterior sheath 1220 can have a bore 1230 which canaccept a bone screw 1240, preferably into the lateral mass or lamina.Alternatively, the bore 1230 can accept any other appropriate and/orequivalent fixation means for fixing the embodiment 1200 to the spine.

FIG. 16 depicts a further preferred embodiment of the present invention.In this embodiment 1300, two joint inserts or inter-facet spacers 1310are positioned in the cervical facet joint 1301. The joint inserts orinter-facet spacers each have outer surfaces 1370 that interact with thebone of the vertebrae forming the cervical facet joint. These outersurfaces 1370 of the embodiment 1300 can be treated to become boneingrowth surfaces 1380, which bone ingrowth surfaces 1380 contribute tostabilizing the two joint inserts or inter-facet spacers 1310 of theimplant 1300. In one preferred embodiment, the bone ingrowth surface1380 can be created with plasma spray titanium, and/or with a coating ofsintered beads. In an alternative preferred embodiment, the implant 1300can have casted porous surfaces 1370, where the porous surface isintegral to the implant 1300. In a further alternative embodiment, thesurfaces 1370 can be roughened in order to promote bone ingrowth intothese defined surfaces of the implants 1300. In other preferredembodiments, the surfaces 1370 can be coated with materials that promotebone growth such as for example BMP, or structural materials such as HA,or other substances which promote growth of bone on other externalsurfaces 1370 of the implant 1300. This fixation stabilizes the implant1300 in the facet joint without fusing the joint, and thus the implantpreserves joint mobility, while accomplishing distraction and increasingforaminal dimension.

Also shown in FIG. 16 are articular inner surfaces 1382 of the implants1300. These surfaces can be formed from a metal and polyethylene, thematerial allowing flexibility and providing for forward bending/flexionand backward extension of the cervical spine. The embodiment 1300 ofFIG. 16 can be made in at least two configurations. The firstconfiguration includes a flexible spacer 1382 made, by way of example,using polyethylene or other suitable, flexible implant material. Theflexible spacer 1382 can be permanently affixed to the upper and lowerjoint insert or inter-facet spacer 1310. The spacer 1382 can be flat orwedge-shaped or have any other shape that would correct the curvature ofthe spine. In other configurations, the spacer 1382 can be affixed toonly the upper insert or inter-facet spacer 1310 or to only the lowerinsert or inter-facet spacer 1310. Alternatively, a spacer 1382 can beaffixed to each of an upper insert or inter-facet spacer 1310 and alower insert or inter-facet spacer 1310 with the upper insert 1310 andthe lower insert or inter-facet spacer 1310 being separate units.

FIG. 17 shows a further preferred embodiment of the implant of thepresent invention. In this embodiment 1400, the implant has a roller1496 mounted on a joint insert or inter-facet spacer 1410, the rollerbeing a further means of preserving joint mobility while accomplishingdistraction. Both the roller 1496 and the joint insert or inter-facetspacer 1410 are positioned in the cervical facet joint 1401. The jointinsert or inter-facet spacer 1410 as in other embodiments has abone-facing surface 1470 and joint articular surface 1482. Thebone-facing surface 1470 can interact with the lower bone of thecervical facet joint 1401. Alternatively, the bone-facing surface caninteract with the upper bone of the cervical facet joint 1401. Betweenthe bone-facing surface 1470 and the joint articular surface 1482 is anaxis about which the roller 1496 can rotate. The roller 1496 rotates ina cavity in the joint insert or inter-facet spacer 1410, and interactswith the top bone of the cervical facet joint 1401. Alternatively, wherethe bone-facing surface 1470 of the joint insert or inter-facet spacer1410 interacts with the top bone of the cervical facet joint 1401, theroller 1496 rotates in a cavity in the joint insert or inter-facetspacer 1410 and interacts with the lower bone of the cervical facetjoint 1401. The rotation of the roller 1496 allows flexion and extensionof the cervical spine. Alternatively, a roller such as roller 1496 canbe secured to an upper and a lower insert such as inserts 410 in FIG. 7.As depicted in FIG. 18, a plurality of rollers 1496 also is possible.

FIG. 19 depicts a further embodiment of the implant of the presentinvention. In this embodiment, two implants 1500 are implanted in thecervical facet joint 1501. Screw fixation or other appropriate fixationis used with implants 1500 for fixation in the cervical facet joint1501. The joint insert or inter-facet spacer 1510 is continuous with aposterior sheath 1520 bent at an angle from the joint insert orinter-facet spacer 1510 to align substantially parallel with the bone,preferably the lateral mass or lamina. The posterior sheath 1520 of eachimplant 1500 can have a bore 1530 which can accept a bone screw 1540,preferably into the lateral mass or lamina. Alternatively, the bore 1530can accept any other appropriate and/or equivalent fixation means forfixing the embodiment 1500 to the spine. The head of the screw 1540 ineach posterior sheath 1520 of each implant 1500 has a groove 1598 orother mechanism for retaining an elastic band 1597. The elastic band1597 is looped around each of the two screws 1540 to restrain movementof the cervical spine without eliminating facet joint mobility. The band1597 preferably can restrain flexion and lateral movement. The elasticband 1597 can be made of a biocompatible, flexible material.

FIG. 20 shows an alternative to use of an elastic band as in FIG. 19. Inthe embodiment in FIG. 20, the elastic band is replaced with a springrestraint 1699, which extends between the heads of two screws 1640, onescrew fixing each of two implants 1600 in the cervical facet joint 1601.

FIG. 21 shows another alternative to using an elastic band and/or aspring as in FIG. 19 or 20. In FIG. 21, magnets 1795 are used forrestraint between the two screws 1740. The magnet 1795 can either becomprised of two opposing magnetic fields or two of the same magneticfields to operate to restrain movement. The head of one of the twoscrews 1740 is magnetized, and the head of the other screw 1740 ismagnetized with either the same or opposite field. If the magnets 1795have the same polarity, the magnets 1795 repel each other and thus limitextension. If the magnets 1795 have opposite polarities, the magnets1795 attract each other and thus limit flexion and lateral movement.

FIGS. 22A-24B, depict a further embodiment 1800 of the implant of thepresent invention. In this embodiment, an artificial facet joint spacer(or insert) or inter-facet spacer (or insert) 1810 is connected with alateral mass plate (also referred to as an anchoring plate) 1820 with ahinge 1822. The hinge 1822 allows the lateral mass plate 1820 to bend ata wide range of angles relative to the artificial facet joint orinter-facet spacer and preferably at an angle of more than 90 degrees,and this flexibility facilitates positioning and insertion of theartificial facet joint spacer or inter-facet spacer 1810 into apatient's facet joint, the anatomy of which can be highly variable amongindividuals. This characteristic also applies to embodiments describedbelow, which have a hinge or which are otherwise enabled to bend by someequivalent structure or material property. The hinge 1822 furtherfacilitates customizing the anchoring of the implant, i.e., thepositioning of a fixation device. The hinge enables positioning of thelateral mass plate 1820 to conform to a patient's cervical spinalanatomy, and the lateral mass plate 1820 accepts a fixation device topenetrate the bone. The artificial facet joint spacer or inter-facetspacer 1810 can be curved or rounded at a distal end 1812 (FIG. 23A),and convex or dome-shaped on a superior surface 1813 to approximate theshape of the bone inside the facet joint. The inferior surface 1815 canbe flat or planar. Alternatively, the inferior surface 1815 can beconcave. As another alternative, the inferior surface 1815 can beconvex.

The lateral mass plate 1820, when implanted in the spine, is positionedoutside the facet joint, preferably against the lateral mass or againstthe lamina. The lateral mass plate 1820 has a bore 1830 therethrough.The bore 1830 can accept a bone screw 1840, also referred to as alateral mass screw, to secure the lateral mass plate 1820 preferably tothe lateral mass or alternatively to another part of the spine, and thusto anchor the implant. The lateral mass screw 1840 preferably has ahexagonal head to accept an appropriately-shaped wrench. As describedbelow, the head accepts a compatible probe 1826 from a locking plate1824.

The locking plate 1824 includes a keel 1828 with a wedge shaped distalend to anchor the implant, preferably in the lateral mass or in thelamina, outside the facet joint and to prevent rotation of the lateralmass plate 1820 and the locking plate 1824. The keel 1828 aligns with agroove 1823 through an edge of the lateral mass plate 1820 to guide andalign the keel 1828 as the keel 1828 cuts into a vertebra.

As noted above, the locking plate 1824 includes a probe 1826 that fitsagainst the head of the lateral mass screw 1840. The locking platefurther includes a bore 1831 that can accept a machine screw (not shown)which passes through to an aligned bore 1829 in the lateral mass plate1820 to hold the locking plate 1824 and the lateral mass plate 1820together without rotational displacement relative to each other. Thelocking plate 1824 thus serves at least two functions: (1) maintainingthe position of the lateral mass screw 1840 with the probe 1826, so thatthe screw 1840 does not back out; and (2) preventing rotation of theimplant with the keel 1828 and machine screw relative to the cervicalvertebra or other vertebrae.

It is to be understood that other mechanisms can be used to lock thelocking plate 1824 to the lateral mass plate 1820. For example, thelocking plate can include a probe with barbs that can be inserted into aport in the lateral mass plate. The barbs can become engaged in ribsthat define the side walls of the port in the lateral mass plate.

In the preferred embodiment depicted in FIGS. 25A, 25B, the lateral massplate 1920 includes a recessed area 1922 for receiving the locking plate1924 so that the locking plate 1924 is flush with the upper surface 1925of the lateral mass plate 1920 when the probe 1926 is urged against thelateral mass screw 1940 and the keel 1928 is inserted into the lateralmass or the lamina of the vertebra. In the preferred embodiment depictedin FIGS. 25A, 25B, the shape and contours of the artificial facet jointspacer or inter-facet joint spacer 1910 can facilitate insertion of theartificial facet joint spacer or inter-facet joint spacer 1910 into thecervical facet joint. In this embodiment, the artificial facet jointspacer or inter-facet joint spacer 1910 has a rounded distal end 1912.The distal end 1912 is tapered in thickness to facilitate insertion. Thetapered distal end 1912 meets and is continuous with a proximalmid-section 1916 which, in this preferred embodiment, has a uniformthickness, and is connected flexibly, preferably with a hinge 1922, tothe lateral mass plate 1920, as described above. The artificial facetjoint spacer or inter-facet joint spacer 1910, with its proximalmid-section 1916 and tapered distal end 1912, is curved downward,causing a superior surface 1913 of the artificial facet joint spacer orinter-facet joint spacer 1910 to be curved. The curve can cause thesuperior surface 1913 to be convex, and the convexity can vary amongdifferent implants 1900 to suit the anatomical structure of the cervicalfacet joint(s) of a patient. An inferior surface 1915 accordingly can bepreferably concave, flat, or convex. The curved shape of the implant canfit the shape of a cervical facet joint, which is comprised of aninferior facet of an upper vertebra and a superior facet of a loweradjacent vertebra. The convex shape of the superior surface 1913 of theartificial facet joint spacer or inter-facet joint spacer 1910 fits witha concave shape of the inferior facet of the upper cervical vertebrae.The concave shape of the inferior surface 1915 of the artificial facetjoint spacer or inter-facet joint spacer 1910 fits with the convex shapeof the superior facet of the cervical vertebrae. The degree of convexityand concavity of the artificial facet joint inferior and superiorsurfaces can be varied to fit a patient's anatomy and the particularpairing of adjacent cervical vertebrae to be treated. For example, aless-curved artificial facet joint spacer or inter-facet joint spacer1910 can be used where the patient's cervical spinal anatomy is sized(as described below) and found to have less convexity and concavity ofthe articular facets. Generally for the same level the input for theright and left facet joint will be similarly shaped. It is expected thatthe similarity of shape of the artificial facet joint spacer orinter-facet joint spacer and the smooth, flush surfaces will allowdistraction of the facet joint without loss of mobility or damage to thebones of the cervical spine. Further, and preferably, the width of themid-section 1916 is from 1.5 mm to 2.5 mm.

Except as otherwise noted above, the embodiment shown in FIGS. 22A-24Bis similar to the embodiment shown in FIGS. 25A, 25B. Accordingly theremaining elements on the 1900 series of element numbers is preferablysubstantially similar to the described elements in the 1800 series ofelement numbers, as set forth above. Thus, by way of example, elements1923, 1928, 1929 and 1930 are similar to respective elements 1823, 1828,1829 and 1830.

FIG. 30 is a flow chart of the method of insertion of an implant of theinvention. The embodiment 1800 or 1900 of the present inventionpreferably is inserted in the following manner (only elements of theembodiment 1800 will be set forth herein, for purposes of the writtendescription of a method of the invention). First the facet joint isaccessed. A sizing tool 2200 (see FIGS. 29A-C) can be inserted to selectthe appropriate size of an implant of the invention for positioning inthe cervical facet joint. This step may be repeated as necessary with,if desired, different sizes of the tool 2200 until the appropriate sizeis determined. This sizing step also distracts the facet joint andsurrounding tissue in order to facilitate insertion of the implant.Then, the artificial facet joint spacer or inter-facet joint spacer 1810is urged between the facets into the facet joint. The facet itself issomewhat shaped like a ball and socket joint. Accordingly, in order toaccommodate this shape, the artificial joint spacer or inter-facet jointspacer 1810 can have a rounded leading edge shaped like a wedge ortissue expander to cause distraction of the facet joint as theartificial facet joint is urged into the facet joint of the spine. Theartificial facet joint spacer or inter-facet joint spacer 1810 alsoincludes the convex surface 1813 in order to more fully accommodate theshape of the facet joint of the spine. However, as set forth above andas depicted in FIG. 25B, it is possible in the alternative to have acurve-shaped artificial facet joint spacer or inter-facet joint spacer1910 with a convex superior surface 1913 and a concave inferior surface1915, the distal end 1912 tapering to facilitate insertion, while theremainder of the artificial facet joint spacer or inter-facet jointspacer 1910, (i.e., the proximal section 1916) has a uniform thickness.

Once the artificial joint spacer or inter-facet joint spacer 1810 ispositioned, the lateral mass plate 1820 is pivoted downward about thehinge 1822 adjacent to the vertebrae and preferably to the lateral massor to the lamina. Thus, the lateral mass plate 1820 may be disposed atan angle relative to the artificial facet joint spacer or inter-facetjoint spacer 1810 for a representative spine configuration. It is to beunderstood that as this embodiment is hinged the final position of thelateral mass plate 1820 relative to the artificial facet joint spacer orinter-facet joint spacer 1810 will depend on the actual spineconfiguration. It is to be understood that embodiments of the inventioncan be made without a hinge, as long as the connection between theartificial facet joint spacer or inter-facet joint spacer and thelateral mass plate is flexible enough to allow the lateral mass plate tobe bent relative to the artificial facet joint spacer or inter-facetjoint spacer in order to fit the anatomy of the patient. Once thelateral mass plate 1820 is positioned, or prior to the positioning ofthe lateral mass plate 1820, a bore can be drilled in the bone toaccommodate the bone screw 1824. Alternatively, the screw 1824 can beself-tapping. The screw is then placed through the bore 1830 and securedto the bone, preferably the lateral mass or the lamina, thereby holdingthe artificial facet joint spacer or inter-facet joint spacer 1810 inplace. In order to lock the bone screw 1824 in place and to lock theposition of the artificial facet joint spacer or inter-facet jointspacer 1810 and the lateral mass plate 1820 in place, the locking plate1824 is positioned over the lateral mass plate 1820. So positioned, theprobe 1826 is positioned through the bore 1830 and against the head ofthe bone screw to keep the bone screw from moving. The keel 1828, havinga sharp chisel-shaped end, preferably can self-cut a groove in the boneso that the keel 1828 is locked into the bone as the keel 1828 isaligned by, and received in, a groove 1831 of the lateral mass plate1820. Alternatively, a groove can be pre-cut in the bone to receive thekeel 1828. As this occurs the bore 1829 of the locking plate 1824 alignswith the threaded bore 1831 of the lateral mass plate 1820 and a machinescrew can be inserted to lock the locking plate relative to the lateralmass plate. This locking prevents the lateral mass plate 1820 and theartificial facet joint spacer or inter-facet joint spacer 1810 fromrotating and, as previously indicated, prevents the bone screw 1840 frombacking out from the vertebra. Preferably the implant is between the C5and C6 vertebrae level, or the C6 and C7 vertebrae level. It is notedthat two implants preferably will be implanted at each level betweenvertebrae. That is, an implant 1800 will be placed in a right facetjoint and also in a left facet joint when viewed from a posterior viewpoint. This procedure can be used to increase or distract the foraminalarea or dimension of the spine in an extension or in neutral position(without having a deleterious effect on cervical lordosis) and reducethe pressure on the nerves and blood vessels. At the same time thisprocedure preserves mobility of the facet joint.

FIGS. 26A-27B show a further embodiment of the implant of the invention,with the embodiment 2000 implanted in the cervical spine as depicted inFIGS. 27A and 27B. The implant 2000 comprises a first artificial facetjoint spacer (or insert) or inter-facet joint spacer (or insert) 2010and a second artificial facet joint spacer or inter-facet joint spacer2010. Each artificial facet joint spacer or inter-facet joint spacer canhave a distal end 2012 that is tapered or wedge-shaped in a way thatfacilitates insertion into the cervical facet joints on both sides oftwo adjacent cervical vertebrae at the same level. The artificial facetjoint spacers or inter-facet joint spacers further can be dome-shaped,or convex on a superior surface 2013, to approximate the shape of thecervical facets of the cervical facet joints.

The first and second artificial facet joint spacers or inter-facet jointspacers 2010 are bridged together by a collar 2015. The collar 2015passes between the spinous processes of the adjacent cervical vertebrae.As can be seen in FIG. 26B, the implant can preferably be “V” shaped or“boomerang” shaped. The entire implant 2000 or the collar 2015 of theimplant can be made of a flexible material such as titanium, so that itis possible to bend the collar 2015 so that it conforms preferably tothe shape of the lateral mass or the lamina of the cervical vertebrae ofthe patient and thereby holds the implant in place with the artificialfacet joint spacers or inter-facet joint spacers 2010 inserted in thecervical facet joints. Bores 2029 are preferably are provided throughimplant 2000 adjacent to the artificial facet joint spacer orinter-facet joint spacer 2010 respectively. These bores 2029 can receivebone screws to position the implant 2000 against the lateral mass or thelamina as shown in FIGS. 27A, 27B. The description of the embodiment2100, in FIGS. 28A, 28B provide further details concerning the method ofaffixing the implant 2000 to the vertebrae. The implant 2100 also can bemade of PEEK or other materials as described herein. Embodiment 2000(the “boomerang” shape depicted in FIG. 27B) further can have a lockingplate as, for example, the locking plate 1824 in FIG. 22A. The lockingplate for embodiment 2000 (not shown) can have the same features aslocking plate 1824, that is: (1) a probe 1826 that interacts with thebone screws to prevent the bone screws from backing out of the bone, thelikely consequence of which would be displacement of the implant 2000;and (2) a keel 1828 with a chisel end to embed in the bone and thus toprevent rotational displacement of the implant. However, given thecollar 2015 configuration of embodiment 2000, a chisel may not serve thesame purpose as with the embodiments set forth above, which lack acollar stabilized by two bone screws. Therefore, a locking plate onembodiment 2000 can be provided without a keel.

FIGS. 28A and 28B depict a further embodiment of the implant of theinvention 2100. In this embodiment 2100, the collar 2115 can be made ofa flexible material such as titanium, of a substantially inflexiblematerial, or of other materials described herein. Substantialflexibility can also be derived from connecting a first artificial facetjoint 2110 with the collar 2115 using a first hinge 2117, and connectinga second artificial facet joint spacer (or insert) or inter-facet jointspacer (or insert) 2110 with the collar 2115 using a second hinge 2117.Using the first hinge 2117 and the second hinge 2117, the collar 2115can be pivoted downward to conform to a particular patient's cervicalspinal anatomy. In other words, the degree of pivoting will vary amongdifferent patients, and the first hinge 2117 and second hinge 2117 allowthe implant 2100 to accommodate the variance.

In the hinged embodiment 2100, and similar to the embodiment 2000, thecollar 2115 can have a first bore 2129 inferior to the first hinge 2117,and a second bore 2129 inferior to the second hinge 2117. A first bonescrew penetrates the first bore 2130 and into the lateral mass or thelamina, and the second bone screw penetrates the second bore 2130 andinto the lateral mass or the lamina, the first and second bone screwsserving to anchor the implant. A bore, preferably in the lateral mass,can be drilled for the first bone screw and for the second bone screw.Alternatively, the bone screws can be self-tapping. A first lockingplate similar to the plate 1924 (FIG. 25A) can be secured about the headof the first bone screw and a second locking plate can be secured aboutthe head of the second bone screw to prevent displacement of the firstand second bone screws 2140. The first locking plate can block the firstbone screw with a probe and the second locking plate can block to thesecond bone screw with a probe.

It should be noted that embodiments 2000 and 2100 also can be configuredfor accommodating treatment of cervical spinal stenosis and othercervical spine ailments where only a single cervical facet joint betweenadjacent vertebrae requires an implant, i.e., where treatment is limitedto one lateral facet joint. In that case, the collar 2015, 2115 extendsmedially without extending further to join a second artificial facetjoint spacer or inter-facet joint spacer 2010, 2110. For the hingedembodiment 2100, the implant comprises a single hinge 2117, and thecollar 2115 has only one bore 2129 to accept one bone screw to securethe implant 2100.

FIGS. 29A-E, depict a sizing and distracting tool 2200 of the invention.Sizing tool 2200 has a handle 2203 and a distal head 2210 that is shapedas an artificial facet joint spacer or inter-facet joint spacer (e.g.,1810) of an implant of the invention. That is, the head 2210 preferablywill have essentially the same features as the artificial facet jointspacer or inter-facet joint spacer 1810, but the dimensions of the head2210 will vary from one tool 2200 to the next, in order to be able touse different versions of the sizing tool 2200 to determine thedimensions of the cervical facet joint that is to be treated and then toselect an appropriately-sized implant. The head 2210 preferably can beused to distract the facet joint prior to the step of implanting theimplant in the facet joint. In this regard, the head 2210 is rounded atthe most distal point 2212, and can be a tapered to facilitate insertioninto a cervical facet joint. The head 2210 also can have a slightlyconvex superior surface 2213, the degree of convexity varying amongdifferent sizing tools 2200 in order to determine the desired degree ofconvexity of an implant to be implanted in the cervical facet joint. Thehead 2210 may have a uniform thickness along a proximal mid-section2216. Accordingly, the inferior surface 2215 preferably can be concave.Alternatively, the proximal mid-section 2212 may be convex on thesuperior surface 1813 without being uniform in thickness. Thus, theinferior surface 2215 can be flat or planar. The head also can becurved.

The head 2210 has a stop 2218 to prevent over-insertion of the head 2210of the sizing tool 2200 into the facet joint. The stop 2218 can be aridge that separates the head 2210 from the handle 2203. Alternatively,the stop 2218 can be any structure that prevents insertion beyond thestop 2218, including pegs, teeth, and the like.

Different sizing tools 2200 covering a range of dimensions of the head2210 can be inserted successively into a cervical facet joint to selectthe appropriate size of an implant to position in the cervical spine,with the appropriate convexity and concavity of artificial facet joint.Each preferably larger head also can be used to distract the facetjoint.

The foregoing description of the present invention has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise forms disclosed.Many modifications and variations will be apparent to practitionersskilled in this art. The embodiments were chosen and described in orderto explain the principles of the invention and its practicalapplication, thereby enabling others skilled in the art to understandthe invention for various embodiments and with various modifications asare suited to the particular use contemplated. It is intended that thescope of the invention be defined by the following claims and theirequivalents.

1. A method for implanting a cervical facet implant in a cervical facetjoint, the method comprising the steps of: accessing a first cervicalfacet joint; urging a facet joint spacer of the implant into the firstcervical facet; positioning a plate, flexibly attached to the facetjoint spacer, relative to the facet joint spacer and against a vertebra;anchoring the plate to the vertebra; positioning a locking plate overthe plate and inserting a keel of the locking plate into the vertebra;and fastening the locking plate to the plate.
 2. The method as in claim1 wherein the inserting step further comprises cutting a groove into alateral mass with the keel.
 3. A method for implanting a cervical facetimplant in a cervical facet joint, the method comprising the steps of:accessing a first cervical facet joint; urging a facet joint spacer ofthe implant into the first cervical facet joint, so that the facet jointspacer positioned in the first cervical facet joint distracts the firstcervical facet joint; positioning a plate flexibly connected to thefacet joint spacer relative to the facet joint spacer and to a vertebra;anchoring the plate of the implant to the vertebra, wherein theapplication of said method increases the foraminal dimension and allowsmobility of the implanted first cervical facet joint; and placing alocking plate over the plate to prevent rotational displacement of theplate.
 4. The method as in claim 3 including inserting a keel of theimplant into the vertebra to prevent rotational displacement of theplate.
 5. A method for implanting a cervical facet implant in a cervicalfacet joint, the method comprising the steps of: accessing a firstcervical facet joint; urging a facet joint spacer of the implant intothe first cervical facet joint; positioning a plate, flexibly attachedto the facet joint spacer, relative to the facet joint spacer andagainst a vertebra by pivoting the plate relative to the facet jointspacer using a hinge that connects the plate to the facet joint spacer;anchoring the plate to the vertebra; positioning a locking plate overthe plate, the positioning step further comprising the steps of:anchoring the plate with a screw; inserting a probe of the locking plateinto a first bore of the plate to block the screw that anchors the plateto the vertebra; embedding a keel of the locking plate into thevertebra; aligning a second bore through the plate with a third bore ofthe locking plate; and securing the locking plate to the plate with asecond screw through the second bore and the third bore.
 6. The methodof claim 5 wherein the embedding and aligning steps occur substantiallysimultaneously.